1. Field of the Invention
The present invention relates to an imaging apparatus and a method for driving the same.
2. Description of the Related Art
For solid-state imaging apparatuses, S/N ratio enhancement and dynamic range expansion have been demanded. To meet such demands, Japanese Patent Application Laid-Open No. 2004-015701 discloses that a detection circuit that detects the levels of pixel signals and an amplifier circuit are provided for each column of pixels arranged in a matrix to control amplification factors for the pixel signals for the respective signals, thereby expanding the dynamic range while maintaining the S/N ratio. Japanese Patent Application Laid-Open No. H11-331709 discloses that data derived by subjecting output signals from an imaging device to A/D conversion to provide signals for a relatively light area, and data derived by subjecting output signals from the imaging device to A/D conversion to provide signals for a relatively dark area are stored in respective memory units and subsequently combined, thereby enabling effective use of the dynamic range of the imaging device.
However, the technique disclosed in Japanese Patent Application Laid-Open No. 2004-015701 requires both a pixel signal level detection unit and a corresponding feedback unit for individually setting an amplification factor for each column of pixels, which may complicate the circuits within the sensor. Furthermore, the amplification factors are controlled based on the detection results, causing a problem in that a time lag equivalent to one frame occurs until reflection of the detection results. Meanwhile, the technique disclosed in Japanese Patent Application Laid-Open No. H11-331709 requires two memory units for storing both images of high intensity correction signals and pixel signals, resulting in an increase in circuit size. The technique also has the problem of an operation speed decrease because pixel signals and high intensity correction signals require exposure and read operations for two frames with different accumulation times.